Of the 12 people arrested over the attack, two have been charged, eight bailed and two released without charge.

Keith Vaz, chairman of the MPs' committee, described Tuesday's session as a "vital opportunity to establish the facts in public".

'More reflective'

Ms Dick, who is head of counter-terrorism for the Met, told MPs 600 police officers had been directly involved in investigating the 25-year-old's killing.

She said 17 addresses and six cars had been searched and police had so far seized 2,649 items of potential evidence, along with an "enormous" amount of digital data and forensic material.

We have a big, changing, morphing threat but I am not going to say the answer is more resources for the policeAssistant Commissioner Cressida Dick

Ms Dick told MPs that police had "no evidence there was anyone else present at the scene".

She said the inquiry was a "police-led investigation" with support from other agencies, such as MI5.

In the days following the attack the Met faced criticism that police armed response teams were slow to reach the scene.

But Ms Dick told MPs: "I do believe our response was very, very good... We were within our response times that we would expect... There was very strong command and control."

She denied a suggestion that police needed greater funding for counter-terrorism resources, and said: "We have a big, changing, morphing threat but I am not going to say the answer is more resources for the police."

Asked if the Met would be better able to counter the threat from terrorism if it had more Muslim officers, she said "We have a very effective service... We would be even more effective if we were more reflective of London's communities."

She said there had been an increase in tension within London's communities but "not so big a rise in attacks that we might have feared".

'Important tool'

Ms Dick would not confirm whether radical preacher Anjem Choudary, a former leader of the now-banned al-Muhajiroun organisation, had been placed under police protection but said that the police were "constantly assessing whether any of his proclamations are breaking the law".

On the issue of a possible renewed attempt to publish a Data Communications Bill, she said "every single counter-terrorism investigation and almost every murder investigation depends on communications data... This is an incredibly important tool and we use it all the time".

Such a bill would give police and security services access to details of all online communication in the UK and supporters say it would help root out would-be terrorists.

The two men accused of murdering Drummer Rigby - Michael Adebolajo, 28, from Romford, east London, and Michael Adebowale, 22, of Greenwich, south-east London - have made separate court appearances.